Friday, November 18, 2011

Antibiotics-producing microorganisms

There has reports mentioned that antibiotic production is a feature of several kinds of soil bacteria and fungi and may represent a survival mechanism whereby organisms can eliminate competition and colonize a niche (Jensen et al., 1997; Talaro and Talaro, 1996). Although both fungal and bacterial species are known to produce antibiotics, fungi tend to produce mostly broad-spectrum activities but more antibiotics are produced by bacteria (Salyers and Whitt, 2001).
Oskay et al. (2004) showed that actinomycetes have the capability to synthesize many different biologically active secondary metabolites such as antibiotics, herbicides, pesticides, anti-parasitic, and enzymes like cellulase and xylanase used in waste treatment. Actinomycetes are the most widely distributed groups of microorganisms in nature. They are attractive, bodacious and charming filamentous gram-positive bacteria. They make up in many cases, especially under dry alkaline conditions, a large part of the microbial population of the soil (Athalye et al., 1981; Goodfellow and Williams, 1983; Lacey, 1973 and 1997; Nakayama, 1981; Waksman, 1961). Based on several studies among bacteria, the actinomycetes are noteworthy as antibiotic producers, making three quarters of all known products, the Streptomyces are especially prolific (Lacey, 1973; Lechevalier, 1989; Locci, 1989; Saadoun and Gharaibeh, 2003; Waksman, 1961).
Actinomycetes can be isolated from soil and marine sediments. The soil actinomycetes have been important sources of antibiotics. For example, about 1% of soil actinomycetes produce streptomycin, first discovered in the 1940s, whereas daptomycin producers were discovered only after screening nearly 107 actinomycetes. Most of the antibiotics in use today are derivatives of natural products of actinomycetes and fungi (Butler and Buss, 2006; Newman and Cragg, 2007). Antibiotics produced by actinomycetes have been evolving for ~1 billion years (Baltz, 2005 and 2006), and fitness has been tested by the ability to penetrate other microbes and inhibit the target enzymes, macromolecules or macromolecular structures (Baltz, 2008).
The ability of actinomycetes to make secondary metabolites with different useful properties is widely exploited. Two thirds of the antibiotics produced by microorganisms are made by actinomycetes. In particular, genus of Streptomyces is remarkable in this aspect, representing about 80% of the actinomycete antibiotics (Borodina et al., 2005).
Microbial natural products are the origin of most of the antibiotics. The discovery of penicillin in the 1940s was followed by the discovery of a huge number of antibiotics from microbes, in particular from members of the actinomycetes and fungi. Actinomycetes have traditionally been the most prolific group in antibiotic production. Fungi are another rich source of antibiotics (Peláez, 2006).
Anupama et al. (2007) reported that actinomycetes have been isolated from different soils, plant materials, water and marine sediments (Mincer et al., 2002). At least 90% of the population among actinomycetes isolated from soils have been reported to be Streptomyces spp. Among microorganisms, actinomycetes are the important source for bioactive metabolites especially antibiotics (Bérdy, 2005).